Non-destructive testing methods using radiation have been and are being broadly employed in various fields extending from various industries to medical applications. An X-ray, for instance, is an electromagnetic wave with a wavelength of about 1 pm to 10 nm (10−12 to 10−8m). X-rays having a short wavelength (about 2 keV˜) are referred to as hard X-rays, whereas those having a long wavelength (about 0.1 keV to about 2 keV) are referred to as soft X-rays.
Absorption contrast techniques that are devised to exploit a difference of absorptive power relative to an X-ray by utilizing a high transmissivity of X-ray can find practical applications such as detection of internal fissures in steel materials and security measures including hand baggage security screenings. On the other hand, X-ray phase contrast imaging of detecting a phase shift of an X-ray caused by a detection object is effective with an object that provides little contrast attributable to X-ray absorption and hence shows a small density difference. Techniques that employ X-ray phase contrast imaging are being studied to find applications such as imaging polymer blends of polymer materials and medical applications.
Among various X-ray phase contrast imaging techniques, PATENT LITERATURE 1 listed below proposes a method that utilizes a refractive effect due to a phase shift caused by a detection object. With this method, an X-ray is generated by an X-ray source and irradiated onto a detection object. Then, the X-ray transmitted through the detection object is discretely focused to a pixel area covering two or more than two pixels on a two-dimensional detector by an X-ray optical means. With such a method, the position of the center of gravity of the focused X-ray can be obtained from the intensity distribution on the pixels covered by the focused X-ray.
While the quantity of refraction of an X-ray due to a detection object is very small, the angle of refraction can be obtained by comparing the position of the center of gravity of the focused X-ray in a state where there is not any detection object and the position of the center of gravity in a state where there is a detection object and determining the quantity of discrepancy between the two positions. Then, as a result, an image relating to the phase shift of an X-ray due to the detection object can be obtained.
Additionally, since the above-described technique directly utilizes the refractive effect of a detection object on X-rays, it is characterized by not requiring highly coherent X-rays such as synchrotron radiations unlike many X-ray phase contrast imaging techniques.